Ammonium nitrate-fuel oil explosive containing anti-static ingredinent



United States Patent 9 Claims. in. 149-41 This invention relates toexplosive compositions comprising ammonium nitrate and a fuel orsensitizer and which are resistant to the development of charges ofstatic electricity.

Explosives composed of ammonium nitrate and oleaginous fuel of the fueloil type are commonly known in the trade as ammonium nitrate-fuel oilexplosives, or simply as AN/F0 explosives. Those of the AN/FO explosiveswhich contain as an additional fuel or sensitizer particulate aluminumor magnesium or alloy thereof are generally referred to as AN/FO/metalexplosives. These explosives are at present widely used in both theconstruction and mining industries.

Originally employed in surface blasting operations such as in quarrying,open pit mining and the like, these types of explosives have now beenintroduced into underground mining operations, which application hasrequired new methods of loading the explosives into boreholes. Whereasin surface blasting operations, the boreholes are normally wide diametervertical holes into which the explosives can be introduced by gravitymethods, the boreholes used in underground mining operations may behorizontal or may be driven into the roof of the working area. Becauseof the granular and free-flowing consistency of AN/FO and AN/ FO/ metalexplosives, it has been necessary to develop means of forcibly injectingthe explosives into the boreholes.

An apparatus now commonly employed for this purpose is a pneumaticallyoperated eductor which discharges the AN/FO or AN/FO/rnetal mixturesinto the boreholes through a tube or hose. However, when the explosivemixtures pass through the eductor and hose, large charges of staticelectricity are developed. These electrical charges have been measuredand in laboratory-simulated borehole loading conditions, charges over20,000 volts have been recorded. This static electricity causesdiscomfort to persons operating the eductor loading apparatus andconstitutes a continuing hazard in an'area where explosives are present.Such charges are capable of etonating electric blasting capsprematurely. Furthermore, they have been shown to be conductible along alength of ordinary safety fuse and are of sufficient intensity todetonate an ordinary blasting cap attached thereto.

The use or presence of electric blasting caps in areas where AN/FO orAN/ FO/ metal explosives are in use has been strongly discouraged andhas, in fact, in many jurisdictions, been prohibited.

It is an object of the present invention to provide a sensitizedammonium nitrate explosive composition which is resistant to thedevelopment of charges of static electricity. Another object of theinvention is to provide a sensitized ammonium nitrate explosivecomposition which, when employed in a pneumatic borehole loadingmachine, will not develop hazardous charges of static electricity.Additional object of the invention will appear hereinafter.

The static-resistant explosive of this invention com- EXPLosrvE3,303,073 Patented Feb. 7, 1967 prises ammonium nitrate, an oleaginousfuel and, optionally, a particulate light metal, and at least oneadditive selected from the group consisting of the products resultingfrom the reaction of a mixture of secondary and tertiary aliphaticamines with a mixture of high molecular weight fatty acids, the additivebeing responsible for the static resistance of the explosive. Inaddition, the explosive compositions may advantageously contain acidacceptors, for example, calcium carbonate, sodium carbonate, ammoniumcarbonate, triethyla-mine or piperidine as a means of absorbing any freenitric acid which may be present in the ammonium nitrate ingredient andwhich may oxidize and destroy the static-proofing ingredient.

The ammonium nitrate ingredient is usually in the form of prills butother physical forms capable of retaining the oleaginous fuel aresuitable. It may be modified by small amounts of materials which impartanti-setting or water-proofiing properties. Examples of such materialsare kiesel uhr, kaolinite, the sodium salt of a mixture of methyl anddimethyl naphthalene, sulphonic acids and calcium stearate. The ammoniumnitrate is suitably present in a concentration ranging from 60 to 98% byweight of the composition. It is, in some cases, advantageous to replacesome, suitably up to 35% of the ammonium nitrate by sodium nitrate.

The oleaginous fuel ingredient of the explosive composition ispreferably diesel oil or fuel oil but other suitable fuels may be usedsuch as lubricating oils, vegetable oils, low melting petroleum greasesand waxes and partially nitrated derivatives of benzene, toluene, xyleneand naphthalene. Suitable amounts of these fuels lie in the range offrom 2% to 20% by weight of the composition. For petroleum hydrocarbons,the preferred amount of fuel is between 4% to 8% by Weight of thecomposition.

The optional particulate light metal ingredient is preferably aluminumor an alloy of aluminum, but magnesium, alloys of magnesium, silicon,ferrosilioon and boron may be used although the latter may prove to bemore expensive, less effective or more difficult to employ from aproduction and safety viewpoint than aluminum or aluminum alloys. Theparticulate metals, when used, may suitably range in particle size froma fine dust to a form not coarser than that which will pass through asize 10 Tyler mesh screen. The aluminum or aluminum alloy is suitablypresent in a concentration ranging from 1 to 25% by weight of thecomposition.

As previously mentioned, the static-proofing ingredient of thecomposition may be any one or a combination of the products resultingfrom the reaction of a mixture of secondary and tertiary aliphaticamines with a mixture of high molecular weight fatty acids, which aminesand acids have the chemical formulae:

in the case of the amines, where R is an aliphatic hydrocarbon grouphaving 1 to 5 carbon atoms, and X is hydrogen or R; and RCOOH in thecase of the fatty acids which are well known materials wherein R is analiphatic hydrocarbon group normally containing between 12 and 20 carbonatoms. Thus the reaction products used as the static-proofingingredients of the compositions of this invention are complex mixturesof secondary amides and amine salts. They are available as items ofcommerce hitherto used only as adhesion improvers in industrial asphaltproducts.

The static-proofing ingredient is preferably used in a concentration offrom 0.05% to 1.0% by weight of the composition.

The acid acceptor ingredient is preferably used in a concentration offrom 0.05 to 0.5% by weight of the composition.

The discovery that the static-proofing ingredient of the compositionprovides the high degree of static generation resistance required in apneumatically loaded explosive composition is most surprising since, asstated above, the ingredient is normally employed as an adhesionimprover in industrial asphalt products.

It has also been surprisingly found that many so-called anti-staticagents commonly employed in the textile, plastics and other industriesto reduce static accumulation are not effective static-proofingingredients in AN/FO and AN/FO/metal explosives. Many of these wellknown anti-static agents produce little or no change in thestatic-generating tendency of AN/FO and AN/ FO/ metal mixtures whileothers have been found to increase the quantity of static electricalbuild-up in pneumatically loaded explosives. Particularly, it has beenfound also that the use of some well known anti-static agents in theseexplosives contribute significantly to the setting-up or caking of theexplosives under conditions of normal storage, thus making theexplosives unsuitable for use.

The explosive composition of this invention is conveniently and simplyprepared by dispersing the staticproofing agent in the oleaginous fueland adding the dispersion to the ammonium nitrate, which may be coatedwith an anti-setting and/ or moisture proofing agent.

Where it is desired to employ a particulate light metal as a sensitizerin addition to the oleaginous fuel, the ammonium nitrate and metal mayfirst be blended together, the oleaginous fuel being then added afterdispersion in the static-proofing agent.

The static-resistant explosive composition of this invention may beprepared in any suitable type of mixing equipment which is adequatelygrounded to earth. Preferably, the mixer should have no rapidly movingparts and have a tumbling action combined with a lifting of the materialfrom the bottom of the mixer to the top to ensure intimate blending. Theconventional ribbon type, zig-zag or rotating plough type mixers aresuitable for this purpose.

As previously mentioned, these compositions have potential uses inblasting operations where the explosive is forced into the boreholethrough a tube or hose, thus introducing the hazard of building upelectrical charges on the hose and the explosive. They are likely to bemost useful in underground blasting operations although they will beuseful also in surface blasting as electrical charges may be producedthrough the tumbling action of the composition in gravity loading ofvertical boreholes.

The invention is further illustrated but not limited by the followingexamples in which parts and percentages are by weight unless otherwisestated.

EXAMPLE 1 An ammonium nitrate-fuel oil blasting composition was preparedby mixing 94 parts of ammonium nitrate prills and 6 parts of diesel oil.A series of mixtures were made up from this composition by addingdefinite percentages of the materials shown in Table I and 100 grams ofeach mixture were then placed in a polythene lines wood drum. The drumwas set rotating at 33 /3 rpm, the explosive composition tumbling overthe polythene lining. Electrical charges generated were picked up bymeans of a metallic probe in contact with the tumbling explosivecomposition and lead to a voltmeter the full range of which was 20volts. The results are given in Table I where the electrical chargegenerated is expressed in terms of the voltage recorded after 10 minutesof tumbling in the drum. Alternatively, where the full volt scalereading was reached before 10 minutes of tumbling, the time required togenerate 20 volts is shown.

Table 1 Age of Charge Explosive Composition Composi- Generated tion(days) (secs) 1 94% ammonium nitrate t. 1 1.5 6% diesel oil 16 1.1 911.8 2 94% ammonium nitrate 14 1 8.7 5.75% diesel oil 84 1 1.7 0.25%antistatic agent* 279 3.9 3 94% ammonium nitrate. 1 1 6.2 5.65% dieseloil 257 1 17.4 0.25% antistatic agent. 0.10% C3003. L 94% ammoniumnitrate 3 2. 1 5.9% diesel oil 98 1. 2 0.1% 02180 355 1. 7

Volts.

*A reaction product of a mixture of secondary and tertiary aliphaticamines with a mixture of high molecular weight fatty acids winch aminesand acids have the chemical formulae previously delmed.

As can be seen from the results shown in Table I, ammonium nitrate/ fueloil explosives composition containing the anti-static additive of thisinvention show a substantial improvement in static generating propertiesover ammonium nitrate/fuel oil compositions devoid of the antistaticadditive. added (Composition 3), the antistatic agent containingcomposition retains its antistatic properties over long periods of time.Composition 4, wherein only the acid acceptor is added to an AN/FOcomposition, is included to demonstrate that the acid acceptor by itselfplays no part in reducing the static generating properties of themixture.

EXAMPLE 2 An ammonium nitrate-fuel oil blasting composition was preparedby the method described in Example 1 and three mixtures were prepared,each containing 0.1% of a well known anti-static agent. The mixtureswere then tumbled in a polythene lined wood drum as in Example 1 and thestatic electricity measured. In Table II the results are expressed onthe basis of 100% for the ammonium nitrate-fuel oil mixture withoutadditive.

Table II Percent static Additive Electricity (1) None 100 (2) 0.1%isopropylamide of dodecyl benzene sulphonic acid 421 (3) 0.1% sorbitanmonopalrnitate 204 (4) 0.1% polyoxyethylene (3.5) tridecyl alcohol Whatwe claim is:

1. An explosive composition resistant to the development of charges ofstatic electricity comprising ammonium nitrate, an oleaginous fuel andat least one additive selected from the group consisting of the reactionproducts of a mixture of secondary and tertiary aliphatic amines with amixture of high molecular weight fatty acids.

2. An explosive composition as claimed in claim 1 wherein sodium nitrateis substituted for part of the ammonium nitrate.

3. An explosive composition as claimed in claim 1 wherein a memberselected from the group consisting of finely divided aluminum and alloysthereof is substituted for part of the ammonium nitrate.

4. An explosive composition as claimed in claim 1 containing an acidacceptor selected from the group consisting of calcium carbonate, sodiumcarbonate, ammonium carbonate, triethylamine and piperidine.

5. An explosive composition resistant to the develop- Similarly, wherean acid acceptor is ment of charges of static electricity comprisingfrom 60% to 90% by weight of ammonium nitrate, from 2% to 20% by weightof an oleaginous fuel and from 0.05% to 1.0% by weight of at least oneadditive selected from the group consisting of the reaction products ofa mixture of secondary and tertiary aliphatic amines with a mixture ofhigh molecular weight-fatty acids.

6. An explosive composition resistant to the development of charges ofstatic electricity comprising from 30% to 96% by weight of ammoniumnitrate, from 1% to 25% by Weight of a member selected from the groupconsisting of finely divided aluminum and alloys thereof,

from 2% to 15% by weight of an oleaginous fuel from to 35% by weight ofsodium nitrate, and from 0.05 to 1.0% by weight of at least one additiveselected from the group consisting of the reaction products of a mixtureof secondary and tertiary aliphatic amines with a mixture of highmolecular weight fatty acids.

7. An explosive composition as claimed in claim 1, wherein the secondaryaliphatic amines have the formula:

wherein R is an aliphatic hydrocarbon group having from 1 to 5 carbonatoms.

8. An explosive composition as claimed in claim 1, wherein the tertiaryaliphatic amines have the formula:

wherein R is an aliphatic hydrocarbon group having from 1 to 5 carbonatoms.

9. An explosive composition as claimed in claim 1, wherein the highmolecular weight fatty acids have the formula:

R'COOH wherein R is an aliphatic hydrocarbon group having from 12 to 20carbon atoms.

10. An explosive composition as claimed in claim 5 wherein the secondaryaliphatic amines have the formula:

wherein R is an aliphatic hydrocarbon group having from 1 to 5 carbonatoms.

11. An explosive composition as claimed in claim 5 wherein the tertiaryaliphatic amines have the formula:

wherein R is an aliphatic hydrocarbon group having from 1 to 5 carbonatoms.

12. An explosive composition as claimed in claim 5 wherein the highmolecular weight fatty acids have the formula:

R'COOH wherein R is an aliphatic hydrocarbon group having from 12 to 20carbon atoms.

13. An explosive composition as claimed in claim 1, wherein theoleaginous fuel is a member selected from the group consisting of liquidpetroleum hydrocarbons, low melting petroleum greases and waxes andpartially nitrated derivatives of benzene, toluene, xylene, andnaphthalene.

14. An explosive composition as claimed in claim 1, wherein the ammoniumnitrate is pre-treated with a member selected from the group consistingof anti-setting and waterproofing agents.

15. An explosive composition as claimed in claim 3 wherein the aluminumingredietn has a particle size not greater than 10 standard Tyler meshsize.

References Cited by the Examiner UNITED STATES PATENTS 2,719,153 9/1955Schulz 14911 X 3,118,797 1/1964 Coffee 14992 X 3,238,076 3/1966 Tayloret al. 14939 X 3,281,292 10/1966 Falconer et al 149-41 X CARL D.QUARFORTH, Primary Examiner.

L. DEWAYNE RUTLEDGE, Examiner.

S. I. LECHERT, JR., Assistant Examiner.

6. AN EXPLOSIVE COMPOSITION RESISTANT TO THE DEVELOPMENT OF CHARGES OFSTATIC ELECTRICITY COMPRISING FROM 30% TO 96% BY WEIGHT OF AMMONIUMNITRATE, FROM 1% TO 25% BY WEIGHT OF A MEMBER SELECTED FROM THE GROUPCONSISTING OF FINELY DIVIDED ALUMINUM AND ALLOYS THEREOF, FROM 2% TO 15%BY WEIGHT OF AN OLEAGINOUS FUEL FROM 0% TO 35% BY WEIGHT OF SODIUMNITRATE, AND FROM 0.05% TO 1.0% BY WEIGHT OF AT LEAST ONE ADDITIVESELECTED FROM THE GROUP CONSISTING OF THE REACTION PRODUCTS OF A MIXTUREOF SECONDARY, AND TERTIARY ALIPHATIC AMINES WITH A MIXTURE OF HIGHMOLECULAR WEIGHT FATTY ACIDS.